Can You Identify This Puzzling Rash?

Can You Identify This Puzzling Rash?

A previously healthy 47-year-old woman presents with an ascending, nonpruritic rash of 3 days' duration on her legs. She reports that the rash began on her ankles following a day of gardening. She does not recall any recent insect bites and denies chest pain, dyspnea, abdominal pain, fever, arthralgia, arthritis, cough, and hemoptysis. She has never had a similar rash before. The patient's only medication is an oral antihistamine for seasonal allergies. She has no known drug allergies.

The diffuse, uniformly distributed maculopapular rash involves the lower extremities bilaterally from the ankles to the knees. The lesions are red and nonblanching, with a central darkened area, and range from 1 to 5 mm in diameter. No lymphadenopathy is noted. Results of chest, cardiac, and abdominal examinations are unremarkable. Laboratory studies reveal an elevated erythrocyte sedimentation rate (34 mm/h) and C-reactive protein level (2.0 mg/dL). Complete blood cell count with differential, comprehensive metabolic panel, prothrombin time, partial thromboplastin time, and international normalized ratio are all within normal limits.

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